264 win mag trouble

OK this will be a long post to fill in the background. I purchased a 264 win mag for a steal ($75) It's a mouser 98 large ring reciever. The rifle had a broken bolt (large crack by the front lug) I replaced the bolt and had a reputable shop check the headspace. I was told "tight but in tolerance" So I bought a few boxes of ammo and started plinking away just to get a feel for it and build up some brass for reloading.

Now here comes the trouble, over half the factory ammo was so over pressured that I couldn't even reprime the brass. The primer pocket was .005 oversize! Visions of a broken bolt flashed through my head! So now I tear down the rifle and start measuring. The first thing I find is there was NO THROAT at all So every round was forced into the rifling with no "jump" at all. No problem right, rented a throater and fixed it right quick!

Reloaded some brass with minimum loads from the book and ta daa seems to be working. Well I didn't want to re-use the brass too much so I picked up a bag of unprimed winchester premium brass. loaded a couple different powders in groups of 4's all minimum loads and back to the shooting bench!

Every new brass round overpressured so bad I gave up after a few shots out of safety. Actually blew the primers right out of the case! Primer pockets were .020 oversize.

Now I'm not a gunsmith by trade but I've been a machinist for 14 years and work as a inspector at an aerospace shop. Very mechanically inclined so tearing apart a bolt action was not a problem. I pulled the barrel from the reciever measured the chamber, picked up a reamer and cleaned it up (in case it was fubared down at the neck) remeasured everything including the reciever down to the bolt face, found out that the head space was off .007 over the nogo spec. Faced the barrel off and reassembled to the reciever. Everything is now perfect!

First round with the new brass at 50 gns powder blows the primer right out! So I load one waaaay down to 20 gns. fire it and it's ok. Take the same case load it up to 60 gns (min spec by book) boom works perfect!

So after all that rambling The main question is why will my rifle which is in perfect spec only fire correctly with "fire formed" brass? I gave all the info to help rule out any easy questions. I also measured the brass and compared it to my old stuff. It was consistant in every way. (weight, wall thickness, volume, dimensionally etc..) So Im hoping someone will recognize something I've missed.

I`ve never even heard of anything like that, but then I`ve only been reloading for about 45 years. I`ve only been playing with wildcats and forming brass for about 20 years, but I`ll try to give you places to look. First I`m use with your back ground that you know that the .264 head spaces on the belt and not the shoulder, but sometimes we over look simple things. Second thing is when fire forming a case lite charges will not fully form them, so I question if your really forming them with a 20 gr. charge of powder. Have you slugged the bore to make sure it is really .264? You have one there that don`t seem to make any sence at all, but if I have any more ideas I`ll try to get them posted.

Oh yeah forgot to mention that step. I did slug the barrel and it's also in spec. I'm not sure how old the gun is the only manf ID says "international" on the barrel itself and I'm unfamilliar with it. I used a crude but functional twist check by measuring out 12" on a cleaning rod and counted the rotations. It has approx 1-10 twist. I'm starting to think this gun had been custom built for a very specific purpose (target or varmint) to use light bullets etc... I'm trying to get it to shoot the 140 gn bullets which are at the top end of the range. Could explain why the throat was so shallow too.

I agree with Tango, STOP! If the results you are getting are that erratic, there is something VERY wrong. Continuing to "experiment" with an explosive device inches from your face will very likely result in the removal of said face.

What powder are you using? What primers? Very light loads can give higher pressures than compressed loads with some powders. How long have you been reloading? There are some complexities that can get you seriously hurt.

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I agree with Tango, STOP! If the results you are getting are that erratic, there is something VERY wrong. Continuing to "experiment" with an explosive device inches from your face will very likely result in the removal of said face.

What powder are you using? What primers? Very light loads can give higher pressures than compressed loads with some powders. How long have you been reloading? There are some complexities that can get you seriously hurt.

I did stop thats why I'm here. As for reloading I've been doing it for ten years. I know not very long compared to some of you (that's also why I'm here)
The problem is not the powder (868 mil surplus) the primer (WLRM) or the bullet 140 gn sierra spitzer (I know cheapies, but I didnt want to waste all the good ones) or the book Lyman #6.

I've been reloading this rifle for a while now without problems. The only time it's presented issues it with "new" or "factory" brass. My 2-3-4th fired brass holds up just fine up to 72 gns of the 868. At that point it shows pressure with squared corner on the primer and a slight "pit" where the pin hit (raised edge)

I can NOT run the same load in a fresh case! when I did it blew the primer right out and ruined the case, not to mention my nerves. Thinking It had to be operator error I loaded 2 more identical rounds (double checked my loads with 2 scales digital and old school rcbs) old and new cases with exactly the same results. Thats when I loaded down the charge to the minimums. When those didn't work either (in the new cases) I examined EVERYTHING in the rifle including mag'ing the bolt for cracks (to restore my faith in it)
So since then:

The same case works flawlessly with IMR 4064 and 4350 (48 and 53 gns respectivly) The same charges in new cases destroys them! The rifle is secured in a shooting bench, sand bagged in, and remotely fired I do understand your need for concern and safety because you never know who you end up talking to on a forum and I do heed your warnings I'd also NEVER do this to someone elses weapon LOL. but since it's mine and only $75...... ummm $250 by now I felt free to figure it out. I've gone through curiosity to puzzlement to frustration to anger back to curiosity now.

Checked every aspect of the new vs old case
weight, volume, neck thickness etc.... only slight variations. the volume was off by 1 gn, neck thickness .002

So while I can make a "safe" load using fire formed brass I'm not happy with that result. I want to know why the new brass will not function properly. It's a HUGE safety issue with me! I know I'm missing something I just don't know what.

Thats where I was going when I tried the IMR 4350 and 4064 both highly reccomended for the caliber but both had exactly the same result as the 868 I currently don't have any of the powders listed but will pick some up when it comes available. I don't know about anywhere else but powder, primers, and cases are still extremly hard to find here.

Yes the 868 is de milled vulcan ammo (ironically my mos in the army was 16R vulcan gunner, I get flashbacks from the smell still ) We found out long ago that the slow burn rate is excellent for magnum rifles and inexpensive in bulk. I've been using it in the fired brass for 2 years now without a problem. I also load 7mm mag and 300 ultra with it all with excellent results.

this to me seems to be one of those conundrums. the weapon works great with any powder in fired brass but over pressures with both factory store bought ammo of any brand (winchester, and remington) and if I load new clean brass

Now todays step was comparing brass on an optical comparator. The neck is slightly shorter with smoother transitions at the angles with the "shoulder" portion slightly longer with less of an angle. The over all case grew .005. I may need to start photo documenting this lol to save my sanity.